This invention relates to priming pumps, and more particularly, it relates to the priming of pumps on fire trucks which use centrifugal water pumps as the means to pressurize and propel the water that is used to extinguish fires. Centrifugal pumps of this type used in the fire trucks are not self-priming and rely on a primer to bring the water to the pump. Typically, this involves pumping from a positive pressure source, like a fire hydrant, or using a primer when drafting water from a pond which is located below the pump.
The most common type of priming device used is a separate positive displacement pump, which evacuates the fire pump and suction line until the air is displaced by water. The prior art in this industry uses a sliding vane type pump which is driven by an electric motor. Other devices used include water-ring primer pumps, piston pumps, gear pumps and exhaust gas-ejector pumps. Each of the priming means just mentioned has varying drawbacks in complexity, cost, reliability, speed, ease of use, freezing, electrical current draw, contamination, installation ease, safety, maximum attainable vacuum, or environmental concerns. The invention disclosed herein is an improvement over the current technology used in fire trucks because of its simplicity, high reliability and performance.
It is an object of this invention to overcome the disadvantages of the prior art and to provide a primer which uses high speed compressed air in a venturi to generate a vacuum to prime a centrifugal pump. It uses compressed air supplied by the air brake compressor of an air-brake fire truck.
This provides for a consistent, highly reliable source of high-pressure air. The high-pressure air flows through a series of venturi (also referred to as ejectors) and is controlled by a valve, which is controlled by either the pump operator or is controlled automatically as part of the entire pumping system. The system is designed with an integral valve that separates the pump from the priming ejectors, and is opened by the compressed air when the primer is activated. The valve closes by a spring return when the air supply is removed. Any water drawn into the primer freely drains by gravity to prevent freezing of the primer in cold weather.
The air valve used is an electric solenoid actuated valve that is tied to a series of switches and sensors that automatically activate the priming system when needed and disengage it when the pump is fully primed. This automatic system may be turned off at the operator""s switch or over-ridden in the xe2x80x9cmanualxe2x80x9d mode of that switch when needed for such operations as inspection and test purposes.